1. Field of the Invention
The present invention relates to a fixing device to be used in an image forming apparatus, and more particularly to the fixing device that can perform a startup operation in a short period of time.
2. Discussion of the Background
A fixing device, which includes a fixing member, a heater to heat the fixing member, a pressing member in press-contact with the fixing member, and a temperature detector to detect a temperature of the fixing member, is commonly known. In the fixing device, energization of the heater is controlled such that the temperature of the fixing member reaches a target temperature based on a detection result of the temperature detector. A recording material bearing an image passes through between the rotating fixing member and the pressing member to fix the image onto the recording material by heat and pressure. The above-described fixing device is commonly used in a multifunctional image forming apparatus having a copier function, a printer function, and a facsimile function, or having at least two of these functions.
In this type of fixing device, the fixing member is heated at a startup period of the fixing device during which the fixing member is heated until it is stably maintained approximately at a target temperature after power to the image forming apparatus is turned on and the heater for the fixing member is energized. When it is detected that the temperature of the fixing member reaches the target temperature, the fixing member and the pressing member start a pre-rotation to make the temperatures of these members uniform before staring a fixing operation of a toner image. When a heater to heat the pressing member is provided, the pressing member is also heated by the heater during a startup period of the fixing device. The fixing member and the pressing member start the pre-rotation when the temperatures of the fixing member and the pressing member reach a respective target temperature suitable for fixing a toner image. When the pre-rotation is started, heat of the fixing member is largely absorbed by the pressing member because the temperature of the pressing member is lower than that of the fixing member. Therefore, the temperature of the fixing member falls below the target temperature again. Thus, the heater keeps on heating the fixing member after the fixing member starts a pre-rotation. When the heater to heat the pressing member is provided, the pressing member is also heated by the heater. When it is detected that the temperatures of the fixing member and the pressing member reach the respective target temperature or higher, the startup operation of the fixing device is finished.
However, when a temperature of the fixing member is controlled at a startup of a fixing device, a longer period of time is required for the startup operation of the fixing device i.e., a longer standby period is required, by which a user is inconvenienced.
The present invention has been made in view of the above-mentioned and other problems and addresses the above-discussed and other problems.
The present invention advantageously provides a novel fixing device wherein a standby period at startup of the fixing device is shortened.
According to an example of the present invention, a fixing device includes a fixing member; a pressing member configured to be in press-contact with the fixing member, wherein the fixing member and the pressing member sandwich a recording material bearing a toner image therebetween while rotating to fix the toner image onto the recording material by heat and pressure; a primary temperature detector configured to detect a temperature of the fixing member; and a primary heater configured to heat the fixing member, wherein energization of the primary heater is controlled such that the temperature of the fixing member reaches a target temperature suitable for fixing a toner image based on a detection result of the primary temperature detector. At startup of the fixing device, the energization of the primary heater is controlled such that the temperature of the fixing member reaches a startup temperature that is higher than the target temperature, and a rotation of the fixing and pressing members is controlled such that the fixing and pressing members start a pre-rotation when the primary temperature detector detects that the temperature of the fixing member reaches the startup temperature.